Abstract: According to some previous studies, slope (a function of reaction time to set size) was decided by the difference between a target and the distractors on feature search of quantitative dimension. However, the difference was confined to specific experimental situations. A hypothesis was that slope was decided by the ratio ( C ) of the difference between a target value ( T) and the distractor values ( D ) to the distractor values according to Weber's law. Slopes between stimuli of different geometrical shapes were not significantly different when corresponding C values were equal. Therefore, circles and triangles were used as stimuli in experiments 1 and 2 respectively. Results supported the above hypothesis. Moreover, a function of slopes to C values was a monotonic decreasing function when target values were bigger than distractor values.

Key words: quantitative dimension, feature search, slope (a function of reaction time to set size)